Single Carrier and Multi-Carrier Frequency Division Multiple Access (FDMA) communication systems, such as Interleaved FDMA, OFDMA, and Discrete Fourier Transform Spread OFDMA communication systems, have been proposed for use in Fourth Generation (4G) communication systems, such as Long Term Evolution (LTE) communication system, for transmission of data over an air interface. In Single Carrier and Multi-Carrier FDMA communication systems, a frequency bandwidth is split into multiple contiguous frequency sub-bands, or sub-carriers, that are transmitted simultaneously. A user may then be assigned one or more of the frequency sub-bands for an exchange of user information, thereby permitting multiple users to transmit simultaneously on the different sub-carriers. To maximize the spectral efficiency, frequencies can be reused between sectors of a cell. As a result, interference from other sectors/cells may occur in this system, and therefore it is important to control user equipment (UE) transmit power levels.
A traditional power control scheme allows an evolved Node B (eNB) of the cell to control the transmit power of UEs under its control by sending transmit power correction (TPC) commands in an uplink scheduling grant sent in a downlink L1/L2 control channel to correct for estimation and accuracy errors. The TPCs received by each UE can be accumulated (to determine the absolute power level relative to a reference level). TPCs are used so that the eNB receives the same power for each served UE. The TPC commands direct that UE to increase or decrease its transmit power to meet these power requirements so as to maintain a target interference level and/or an average system performance level.
However, there may be instances where a UE will not receive these TPC commands from the eNB. This is especially true for UEs at the edge of a cell or at bad coverage locations resulting in severely limited RF channel conditions, such as during deep-fade scenarios. Losing TPC bits in a channel due to RF conditions can lead to a power misalignment between the UE and the eNB. For example, an eNB could think that the UE is transmitting at a maximum transmitter power, but the UE could actually be transmitting at a lower power level, or vice versa. Without proper agreement between a UE and eNB, one or the other could end up transmitting at full power resulting in additional interference in the system.
One solution to the problem is to communicate absolute TPC bits instead of accumulated TPC bits. In this way, when the UE reconnects it will know exactly which absolute transmitter power to use. However, switching back and forth between using absolute or accumulated TPC bits requires layer 2 messages and will take additional time. Even so, such instructions may not reach to the UE due to the same poor channel conditions that made the UE lose the TPC bits in the first place.
Another solution to the problem is to use a separate over the air message (either broadcast or UE specific) to realign the power level. Again this requires additional messaging and time, and such messages may not reach to the eNB due to the same poor channel conditions.
Still another solution is for the eNB to stop TPC bit generation when an accumulation of TPC bits reaches a power level threshold. However, this solution then assume subsequent TPC bit generation corresponding to a 0 dB adjustment, which may be a completely incorrect assumption.
Therefore, a need exists for an uplink power alignment estimate technique to address the situation where TPC bits are lost, without the need to utilize additional messaging.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and that common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.